Proximal Humerus Fractures

In utero, the arm bud appears 26 days after fertilization and 24 hours before the appearance of the leg bud.1 The process of chondrification in the upper limb precedes ossification and starts with the humerus at day 36. The osteochondral ossification begins as early as day 54, and the proximal humerus develops from three distinct ossification centers, including one for the humeral head and each one for the lesser and greater tuberosity. The ossification center for the humeral head appears at 4 to 6 months postconception. However, the proximal humerus is still primarily cartilaginous at birth. The ossification center for the greater tuberosity arises during the third year of age, and the lesser tuberosity ossification center appears by the fifth year. All these ossification centers fuse together by age of 17 to form the head of the humerus. By the age of 19, the head and shaft have fused together. The fusion of the ossification centers creates a weakened area in the construct, known as the epiphyseal scar, which is more susceptible to fracture.3 The four-segment system developed by Charles Neer classifies proximal humerus fractures according to affected epiphyseal scars and is commonly used to address management and prognosis of these lesions.4,5